This application relates generally to data storage devices and more particularly to an apparatus and method for improving disc drive actuator servo performance.
Computers commonly use disc drives or tape drives to store large amounts of data in a form that can be readily accessed by a user. A disc drive generally includes a stack of vertically spaced magnetic discs that are rotated at high speed by a spindle motor. The surface of each disc is divided into a series of concentric, radially spaced data tracks in which the data are stored in the form of magnetic flux transitions. Typically, each data track is divided into a number of data sectors that store data blocks of a fixed size.
Data are stored and accessed on the discs by an array of read/write heads mounted to a rotary actuator assembly, or xe2x80x9cE-block.xe2x80x9d Typically, the E-block includes a plurality of actuator arms which project outwardly from an actuator body to form a stack of vertically spaced actuator arms. The stacked discs and arms are configured so that the surfaces of the stacked discs are accessible to the heads mounted on the interleaved stack of actuator arms.
Head wires included on the E-block conduct electrical signals from the heads to a flex circuit, which in turn conducts the electrical signals to a flex circuit bracket mounted to a disc drive basedeck. For a discussion of some modern E-block assembly techniques, see U.S. Pat. No. 5,404,636 entitled xe2x80x9cMethod of Assembling a Disk Drive Actuatorxe2x80x9d issued Apr. 11, 1995 to Stefansky et al., and assigned to the assignee of the present invention.
The actuator body pivots about a cartridge bearing assembly which is mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The actuator assembly includes a voice coil motor which enables the actuator arms and the heads attached thereto to be rotated about the cartridge bearing assembly so that the arms move horizontally (i.e. in a plane parallel to the surfaces of the discs) to selectively position a head adjacent to a preselected data track.
The voice coil motor includes a coil mounted radially outwardly from the cartridge bearing assembly, the coil being immersed in the magnetic field of a magnetic circuit of the voice coil motor. The magnetic circuit comprises one or more permanent magnets and magnetically permeable pole pieces. When current is passed through the coil, an electromagnetic field is established which interacts with the magnetic field of the magnetic circuit so that the coil moves in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces.
Each of the heads is mounted to an actuator arm by a flexure which attaches to the end of the actuator arm. Each head includes an interactive element such as a magnetic transducer which either senses the magnetic transitions on a selected data track to read the data stored on the track, or transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the data track. Air currents are caused by the high speed rotation of the discs. A slider assembly included on each head has an air bearing surface which interacts with the air currents to cause the head to fly at a short distance above the data tracks on the disc surface.
There is a generally recognized trend in the industry to increase track density, making more and more accurate track following necessary. At the same time, increasing disc rotation speeds have resulted in more and more noise energy being transferred to each arm and head-gimbal assembly by wind. This acts as a disturbance having energy distributed across a wide spectrum of frequencies. This makes accurate track following difficult, especially when it includes significant energy at any of the resonance frequencies of the arms. Thus, there is a need for an improved technique for reducing wind-induced disturbances upon arms and head-gimbal assemblies of the disc drive.
Meanwhile, there has been a trend among disc drive manufacturers to construct drives of various capacities, for a given housing size or xe2x80x9cform factor.xe2x80x9d Once a design is complete for a xe2x80x9cfully populatedxe2x80x9d disc drive, one or more modified designs of so-called xe2x80x9cde-populatedxe2x80x9d disc drives are hastily generated. This widespread approach merely scales down the fully populated design, failing to recognize the synergy achievable by optimizing a de-populated design. Thus, there is a need for ways to take appropriate advantage of this opportunity.
The present invention provides a solution to these and other problems, and offers other advantages over the prior art.
It has been observed that disc drives with more than one disc show considerably more non-repeatable runout (NRRO) on inner heads (i.e. between discs). To alleviate this, an original multi-disc design is adapted by (a) reducing the number of discs in the stack and (b) configuring the drive of the adapted design with a larger nominal inter-disc separation than that of the original design. In one embodiment, the larger separation is maintained by an increased number of disc spacers between each consecutive pair of the discs in the disc stack of the modified design. The result of such a design adaptation is a disc drive with better performance characteristics than would exist by the original design. For example, because of a reduced level of windage-induced NRRO, the disc drive of the adapted design can permit data tracks servo-written at a higher density than would otherwise be feasible.
These and various other features as well as additional advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.